Feeding rate in adult Manduca sexta is unaffected by proboscis submersion depth.

Adult moths from framily Spingidae (i.e. hawkmoths or sphinx moths) commonly feed on flower nectar through an extended proboscis, often several centimeters in length and longer than the body of the moth. Feeding on a viscous liquid (nectar) through a long and narrow tube is a challenging fluid dynamic problem and the subject of long-running scientific investigation. Here we characterized the relationship between proboscis submergence depth and nectar drinking rate in Manduca sexta hawkmoths. Video recordings of moth feeding bouts were collected and neural networks were used to extract data by object localization, tracking the location of the nectar meniscus and moths' proboscis tips. We found that although feeding rates vary among bouts, the variation was not associated with proboscis submergence depth. These results show that despite the theoretical possibility of fluid uptake through the walls of the proboscis, such effects do not have a substantial effect on nectar uptake rate, and suggest that nectar must traverse the full length of the proboscis.

Intermediate-Term Clinical Outcomes of High-Density Autologous Chondrocyte Implantation in Patients with Concomitant Anterior Cruciate Ligament Reconstruction and Focal Chondral Lesions.

OBJECTIVE: To investigate intermediate-term clinical results in patients with concomitant anterior cruciate ligament (ACL) reconstruction and chondral defect treated with high-density autologous chondrocyte implantation (HD-ACI) compared to patients without ACL tear but with a chondral lesion and HD-ACI treatment. DESIGN: Forty-eight patients with focal chondral lesions underwent HD-ACI (24 with ACL reconstruction after an ACL injury and 24 with an intact ACL). Follow-up assessments occurred at 6, 12, and 24 months. Patient-reported knee function and symptoms were assessed using the International Knee Documentation Committee (IKDC) questionnaire, pain was measured using the Visual Analog Scale (VAS), and adverse events were monitored. Physical activity was assessed using the Tegner Activity Level Scale, and cartilage healing was evaluated with the Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score. RESULTS: No significant adverse events occurred during follow-up. Both groups showed significant improvements at 2 years compared to baseline (VAS: 8.0 ± 1.3 to 1.4 ± 2.0 [normal ACL]; 7.4 ± 2.3 to 2.1 ± 2.3 [ACL reconstruction]; IKDC: 39.2 ± 10.6 to 76.1 ± 22.0 [intact ACL]; 35.6 ± 12.1 to 74.6 ± 20.9 [ACL reconstruction]). Patients in both groups exceeded the minimal clinically important difference (MCID) for IKDC scores. The Tegner Activity Level Scale decreased immediately after surgery and increased after 2 years, with 70.6% (normal ACL) and 89.5% (ACL reconstruction) returning to their preinjury activity levels. No significant differences in the MOCART score were observed between the groups. CONCLUSIONS: ACL reconstruction does not appear to reduce the outcomes (at 2 years) of HD-ACI.

Electrodeposited MoxSyOz/Ni Tribological Coatings.

Deposition of molybdenum disulfide (MoS2) coatings using physical vapor deposition (PVD) and mechanical burnishing has been widely assessed for solid lubricants in space applications but still suffers from line-of-sight constraints on complex geometries. Here, we highlight one of the first demonstrations of electrodeposited MoxSyOz and MoxSyOz/Ni thin-film coatings from aqueous solutions of ammonium tetrathiomolybdate for solid lubricant applications and their remarkable ability to provide low coefficients of friction and high wear resistance. Characterization of the coating morphology shows amorphous microstructures with a high oxygen content and cracking upon drying. Even so, electrodeposited MoxSyOz can achieve low steady-state coefficients of friction (µ ∼ 0.05-0.06) and wear rates (2.6 × 10-7 mm3/(N m)) approaching those of physical vapor deposited coatings (2.3 × 10-7 mm3/(N m)). Additionally, we show that adding dopants such as nickel increased the wear rate (7.5 × 10-7 mm3/(N m)) and initial coefficient of friction (µi = 0.23) due to compositional modifications such as dramatic sub-stoichiometry (S/Mo ∼ 1) and expression of a NiOx surface layer, although doping did reduce the degree of cracking upon drying.

Water adsorption on MoS2 under realistic atmosphere conditions and impacts on tribology.

Molybdenum disulfide (MoS2) is a 2D material widely used as a dry lubricant. However, exposure to water and oxygen is known to reduce its effectiveness, and therefore an understanding of the uptake of water is important information for mitigating these effects. Here we use grand canonical Monte Carlo simulations to rigorously study water adsorption on MoS2 surfaces and edges with different concentrations of defects under realistic atmospheric conditions (i.e. various temperatures and humidity levels). We find that the amount of water adsorbed depends strongly on the number of defects. Simulations indicate that defect sites are generally saturated with water even at low ppm levels of humidity. Water binds strongly to S vacancies on interlamellar surfaces, but generally only one water molecule can fit on each of these sites. Defects on surfaces or edges of lamellae also strongly attract water molecules that then nucleate small clusters of water bonded via hydrogen bonding. We demonstrate that water preferentially binds to surface defects, but once those are saturated at a critical humidity level of about 500-1000 ppm water, water binds to edge sites where it negatively impacts the tribological performance of MoS2.

Solvent-cast 3D printing with molecular weight polymer blends to decouple effects of scaffold architecture and mechanical properties on mesenchymal stromal cell fate.

The biochemical and physical properties of a scaffold can be tailored to elicit specific cellular responses. However, it is challenging to decouple their individual effects on cell-material interactions. Here, we solvent-cast 3D printed different ratios of high and low molecular weight (MW) poly(caprolactone) (PCL) to fabricate scaffolds with significantly different stiffnesses without affecting other properties. Ink viscosity was used to match processing conditions between inks and generate scaffolds with the same surface chemistry, crystallinity, filament diameter, and architecture. Increasing the ratio of low MW PCL resulted in a significant decrease in modulus. Scaffold modulus did not affect human mesenchymal stromal cell (hMSC) differentiation under osteogenic conditions. However, hMSC response was significantly affected by scaffold stiffness in chondrogenic media. Low stiffness promoted more stable chondrogenesis whereas high stiffness drove hMSC progression toward hypertrophy. These data illustrate how this versatile platform can be used to independently modify biochemical and physical cues in a single scaffold to synergistically enhance desired cellular response.

Sarcoma sinovial primario de pericardio / Primary pericardial synovial sarcoma

Resumen El sarcoma sinovial primario del pericardio es un tumor muy raro y de mal pronóstico y se sabe poco en cuanto al manejo terapéutico. Presentamos el caso de una paciente de 51 años a quien se le realizó resección quirúrgica incompleta, quimioterapia y radioterapia. Hasta donde sabemos, este es el primer caso de un sarcoma sinovial primario de pericardio que luego de operado se mantuvo asintomático durante 5 años hasta que en una TAC de control se le detectaron metástasis cardiacas que comprometían las cavidades derechas y con quimioterapia, la ecocardiografía demostró la reso lución completa de las mismas.

Abstract Primary pericardial synovial sarcoma is an extraor dinarily very rare tumor with a poor prognosis, and little is known about its therapeutic management. We describe the case of a 51-year-old woman patient who underwent incomplete surgical resection, chemotherapy, and radiotherapy. To the best of our knowledge, no pri mary pericardial synovial sarcoma has been described which, after surgery, remains asymptomatic for 5 years, and until a control CT scan detects cardiac metastases that compromised the lumen of the right cavities and with chemotherapy, echocardiography demonstrated complete resolution of cardiac metastases.

[Primary pericardial synovial sarcoma]. / Sarcoma sinovial primario de pericardio.

Primary pericardial synovial sarcoma is an extraordinarily very rare tumor with a poor prognosis, and little is known about its therapeutic management. We describe the case of a 51-year-old woman patient who underwent incomplete surgical resection, chemotherapy, and radiotherapy. To the best of our knowledge, no primary pericardial synovial sarcoma has been described which, after surgery, remains asymptomatic for 5 years, and until a control CT scan detects cardiac metastases that compromised the lumen of the right cavities and with chemotherapy, echocardiography demonstrated complete resolution of cardiac metastases.

El sarcoma sinovial primario del pericardio es un tumor muy raro y de mal pronóstico y se sabe poco en cuanto al manejo terapéutico. Presentamos el caso de una paciente de 51 años a quien se le realizó resección quirúrgica incompleta, quimioterapia y radioterapia. Hasta donde sabemos, este es el primer caso de un sarcoma sinovial primario de pericardio que luego de operado se mantuvo asintomático durante 5 años hasta que en una TAC de control se le detectaron metástasis cardiacas que comprometían las cavidades derechas y con quimioterapia, la ecocardiografía demostró la resolución completa de las mismas.

Arginine Residues Modulate the Membrane Interactions of pHLIP Peptides.

Most processes at the water-membrane interface often involve protonation events in proteins or peptides that trigger important biological functions and events. This is the working principle behind the pHLIP peptide technology. A key titrating aspartate (Asp14 in wt) is required to protonate to induce the insertion process, increase its thermodynamic stability when membrane-embedded, and trigger the peptide's overall clinical functionality. At the core of pHLIP properties, the aspartate pKa and protonation are a consequence of the residue side chain sensing the changing surrounding environment. In this work, we characterized how the microenvironment of the key aspartate residue (Asp13 in the investigated pHLIP variants) can be modulated by a simple point mutation of a cationic residue (ArgX) at distinct sequence positions (R10, R14, R15, and R17). We carried out a multidisciplinary study using pHRE simulations and experimental measurements. Fluorescence and circular dichroism measurements were carried out to establish the stability of pHLIP variants in state III and establish the kinetics of the insertion and exit of the peptide from the membrane. We estimated the contribution of the arginine to the local electrostatic microenvironment, which promotes or hinders other electrostatic players from coexisting in the Asp interaction shell. Our data indicate that the stability and kinetics of the peptide insertion and exit from the membrane are altered when Arg is topologically available for a direct salt-bridge formation with Asp13. Hence, the position of arginine contributes to fine-tuning the pH responses of pHLIP peptides, which finds wide applications in clinics.

Spectroscopic Evaluation of Surface Chemical Processes Occurring in MoS2 upon Aging.

Molybdenum disulfide (MoS2) coatings have attracted widespread industrial interest owing to their excellent lubricating properties under vacuum and inert conditions. Unfortunately, the increase in MoS2 interfacial shear strength following prolonged exposure to ambient conditions (a process referred to as "aging") has resulted in reliability issues when MoS2 is employed as solid lubricant. While aging of MoS2 is generally attributed to physical and chemical changes caused by adsorbed water and/or oxygen, a mechanistic understanding of the relative role of these two gaseous species in the evolution of the surface chemistry of MoS2 is still elusive. Additionally, remarkably little is known about the effect of thermally- and tribologically-induced microstructural variations in MoS2 on the aging processes occurring in the near-surface region of the coating. Here, we employed three analytical techniques, namely, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and grazing-incidence X-ray diffraction (GIXRD), to gain insights into the aging phenomena occurring in sputtered MoS2 coatings before and after tribological testing, while also evaluating the impact of thermally-induced variations in the coating structure on aging. The outcomes of XPS analyses provide evidence that a substantial surface oxidation of MoS2 only takes place under humid conditions. Furthermore, the correlation of XPS, ToF-SIMS, and GIXRD results allowed for the development of a qualitative model for the impact of shear-induced microstructural variations in MoS2 on the transport of water in the near-surface region of this material and on the extent of surface oxidation. These results add significantly to our understanding of the aging mechanisms of MoS2 coatings used in tribological applications and their dependence on environmental conditions.

Characterizing properties of scaffolds 3D printed with peptide-polymer conjugates.

Three-dimensional (3D) printing is a popular biomaterials fabrication technique because it enables scaffold composition and architecture to be tuned for different applications. Modifying these properties can also alter mechanical properties, making it challenging to decouple biochemical and physical properties. In this study, inks containing peptide-poly(caprolactone) (PCL) conjugates were solvent-cast 3D printed to create peptide-functionalized scaffolds. We characterized how different concentrations of hyaluronic acid-binding (HAbind-PCL) or mineralizing (E3-PCL) conjugates influenced properties of the resulting 3D-printed constructs. The peptide sequences CGGGRYPISRPRKR (HAbind-PCL; positively charged) and CGGGAAAEEE (E3-PCL; negatively charged) enabled us to evaluate how conjugate chemistry, charge, and concentration affected 3D-printed architecture, conjugate location, and mechanical properties. For both HAbind-PCL and E3-PCL, conjugate addition did not affect ink viscosity, filament diameter, scaffold architecture, or scaffold compressive modulus. Increasing conjugate concentration in the ink prior to printing correlated with an increase in peptide concentration on the scaffold surface. Interestingly, conjugate type affected final conjugate location within the 3D-printed filament cross-section. HAbind-PCL conjugates remained within the filament bulk while E3-PCL conjugates were located closer to the filament surface. E3-PCL at all concentrations did not affect mechanical properties, but an intermediate HAbind-PCL concentration resulted in a moderate decrease in filament tensile modulus. These data suggest final conjugate location within the filament bulk may influence mechanical properties. However, no significant differences were observed between PCL filaments printed without conjugates and filaments printed with higher HAbind-PCL concentrations. These results demonstrate that this 3D printing platform can be used to functionalize the surface without significant changes to the physical properties of the scaffold. The downstream potential of this strategy will enable decoupling of biochemical and physical properties to fine-tune cellular responses and support functional tissue regeneration.

Subcostal right ventricular free wall strain in patients with pulmonary hypertension / Strain subcostal de la pared libre del ventriculo derecho en pacientes con hipertensión pulmonar

Abstract Right ventricular longitudinal strain (RVLS) is frequently used as a measure of right ventricular systolic function. Abnormal RV strain is associated with poor prognosis in patients with pulmonary hyper tension (PH); however, the measure is not always easy to obtain in patients with poor apical acoustic windows. Objective: This study aims to analyze the RVLS and determine if there is a difference when measured from the apical and subcostal views. Methods: In this cross-sectional study, we analyzed 22 adult outpatients (≥ 18 years old), 81% female, mean age 49.9 ± 17.3 years, with a diagnosis of PH using right heart catheterization, followed from January 2016 to January 2020. Results: RVLS measured in the RV free wall from the apical views was -15% (-19% to -10%) and subcostal views -14.5% (-18% to -11%) were highly correlated (Person's r = 0.969, p < 0.0001). Segment by segment analysis did not show significant differences either: basal four-chamber vs. sub costal view was -16.5% (-21% to -11%) vs. -15.5% (-20% to -11%), p = 0.99, mid four-chamber view vs. subcotal view was -16.5% (-21% to -12%) vs. -16.5% (-20% to -11%), p = 0.87, apical four-chamber view vs. subcostal view was -12% (-18% to -8%) vs. -13.5% (-19% to -10%), p = 0.93. Conclusion: Subcostal RVLS free wall is a feasible and accurate alternative to conventional RVLS free wall from the apical view in patients with pulmonary hypertension and could be useful in patients with poor acoustic apical four-chamber windows.

Resumen El strain longitudinal del ventrículo derecho (SLVD) permite medir la función sistólica del ventrículo derecho (VD). La disminución del strain (deformación) del VD se asocia con mal pronóstico en pacientes con hipertensión pulmonar (HP), pero no siempre es fácil de obtener en pacientes con mala ventana acústica apical. Objetivo: Este estudio tiene como objetivo analizar el SLVD y determinar si las vistas apical y subcostal son comparables. Métodos: En este estudio transversal, se incluyeron 22 pacientes adultos ambulatorios (≥18 años), 81% mujeres, edad promedio 49.9 ± 17.3 años, con diagnóstico de HP mediante cateterismo cardíaco derecho, seguidos desde enero de 2016 hasta enero de 2020. Se midió la deformación de la pared libre del ventrículo derecho desde las vistas de cuatro cámaras apical y cuatro cámaras subcostal. Resultados: El SLVD medido en la pared libre del VD desde la vista apical fue -15% (-19% a -10%) vs. -14.5% (-18% a -11%) cuando se midió desde la vista subcostal (p = 0,99). El análisis segmento por s egmento tampoco mostró diferencias significativas: el segmento basal apical vs. subcostal fue -16.5% (-21% a -11%) vs. -15.5% (-20% a -11%), p = 0.99, el segmento medio apical vs. la vista subcotal fue -16.5% (-21% a -12%) vs. a -16.5% (-20% a -11%), p = 0.87, el segmento apical vs. la vista subcostal fue -12% (-18% a -8%) frente a -13.5% (-19% a -10%), p = 0.93. Conclusión: En pacientes con HP, el SLVD obtenido en la pared libre subcostal es una alternativa útil en los casos con ventana acústica apical subóptima.

High-Sensitivity Low-Energy Ion Spectroscopy with Sub-Nanometer Depth Resolution Reveals Oxidation Resistance of MoS2 Increases with Film Density and Shear-Induced Nanostructural Modifications of the Surface.

For decades, density has been attributed as a critical aspect of the structure of sputter-deposited nanocrystalline molybdenum disulfide (MoS2) coatings impacting oxidation resistance and wear resistance. Despite its importance, there are few examples in the literature that explicitly investigate the relationship between the density and oxidation behaviors of MoS2 coatings. Aging and oxidation are primary considerations for the use of MoS2 coatings in aerospace applications as they inevitably experience prolonged storage in water and oxygen-rich environments prior to use. Oxidation that is either limited to the first few nanometers or through the bulk of the coating can result in seizure due to high initial coefficients of friction or component failure from excessive wear. High-sensitivity low-energy ion spectroscopy (HS-LEIS) and Rutherford backscattering spectrometry (RBS) are both used to understand the extent of oxidation throughout the first ∼10 nanometers of the surface of pure sputtered nanocrystalline MoS2 coatings after high-temperature aging and how it is impacted by the density of coatings as measured by RBS. Results show that low-density coatings (ρ = 3.55 g/cm3) exhibit a more columnar microstructure and voiding, which act as pathways for oxidative species to penetrate and interact with edge sites, causing severe surface and subsurface oxidation. Furthermore, HS-LEIS of surfaces sheared prior to oxidation reveals that the oxidation resistance of low-density MoS2 coatings can be significantly improved by shear-induced reorientation of the surface microstructure to a basal orientation and elimination of pathways for oxygen into the bulk through compaction of surface and subsurface voids.

Malnutrition and sarcopenia worsen short- and long-term outcomes in internal medicine inpatients.

PURPOSE: This work aims to describe patients hospitalized in internal medicine wards in terms of nutrition and sarcopenia. It also seeks to evaluate short- and long-term mortality related to malnutrition and sarcopenia. METHODS: This cross-sectional study collected data on consecutive patients admitted to a single center's internal medicine ward. Patients were recruited in May and October 2021. Malnutrition was determined by the Mini-Nutritional Assessment-Short Form (MNA-SF) and sarcopenia by the Strength, Assistance in walking, Rise from a chair, Climb stairs, and Falls questionnaire (SARC-F scale) and handgrip strength test. Patients who were hospitalized for >48 hours were excluded. RESULTS: The sample included 619 patients with a mean ± SD age of 76.0 ± 14.8 years of which 50.6% were women. Patients were classified into three groups based on malnutrition: group 1 (MNA-SF 12-14 points) (no risk) included 158 patients, group 2 (MNA-SF 8-12 points) (high risk) included 233 patients, and group 3 (MNA-SF 0-7 points) (malnourished) included 228 patients. Malnourished patients had more dysphagia, significantly lower protein and albumin levels, and significantly higher inflammatory marker levels and pressure ulcers. In-hospital mortality was significantly higher in groups 2 and 3 (p < .00001). The worst outcome (mortality and readmissions or mortality) was more common among malnourished patients (p = .0001). Inflammation, comorbidity, and sarcopenia were most closely associated with negative outcomes. CONCLUSION: Malnutrition upon admission is associated with worse short- and long-term outcomes in internal medicine inpatients. Sarcopenia, multimorbidity, and inflammation-measured by albumin, C-reactive protein, or their ratios-are key risk factors. Early identification of malnutrition and sarcopenia through active screening is important in caring for internal medicine patients.

Subcostal right ventricular free wall strain in patients with pulmonary hypertension.

Right ventricular longitudinal strain (RVLS) is frequently used as a measure of right ventricular systolic function. Abnormal RV strain is associated with poor prognosis in patients with pulmonary hypertension (PH); however, the measure is not always easy to obtain in patients with poor apical acoustic windows. OBJECTIVE: This study aims to analyze the RVLS and determine if there is a difference when measured from the apical and subcostal views. METHODS: In this cross-sectional study, we analyzed 22 adult outpatients (= 18 years old), 81% female, mean age 49.9 ± 17.3 years, with a diagnosis of PH using right heart catheterization, followed from January 2016 to January 2020. RESULTS: RVLS measured in the RV free wall from the apical views was -15% (-19% to -10%) and subcostal views -14.5% (-18% to -11%) were highly correlated (Person's r = 0.969, p < 0.0001). Segment by segment analysis did not show significant differences either: basal four-chamber vs. subcostal view was -16.5% (-21% to -11%) vs. -15.5% (-20% to -11%), p = 0.99, mid four-chamber view vs. subcotal view was -16.5% (-21% to -12%) vs. -16.5% (-20% to -11%), p = 0.87, apical four-chamber view vs. subcostal view was -12% (-18% to -8%) vs. -13.5% (-19% to -10%), p = 0.93. CONCLUSION: Subcostal RVLS free wall is a feasible and accurate alternative to conventional RVLS free wall from the apical view in patients with pulmonary hypertension and could be useful in patients with poor acoustic apical four-chamber windows.

El strain longitudinal del ventrículo derecho (SLVD) permite medir la función sistólica del ventrículo derecho (VD). La disminución del strain (deformación) del VD se asocia con mal pronóstico en pacientes con hipertensión pulmonar (HP), pero no siempre es fácil de obtener en pacientes con mala ventana acústica apical. Objetivo: Este estudio tiene como objetivo analizar el SLVD y determinar si las vistas apical y subcostal son comparables. Métodos: En este estudio transversal, se incluyeron 22 pacientes adultos ambulatorios (=18 años), 81% mujeres, edad promedio 49.9 ± 17.3 años, con diagnóstico de HP mediante cateterismo cardíaco derecho, seguidos desde enero de 2016 hasta enero de 2020. Se midió la deformación de la pared libre del ventrículo derecho desde las vistas de cuatro cámaras apical y cuatro cámaras subcostal. Resultados: El SLVD medido en la pared libre del VD desde la vista apical fue -15% (-19% a -10%) vs. -14.5% (-18% a -11%) cuando se midió desde la vista subcostal (p = 0,99). El análisis segmento por s egmento tampoco mostró diferencias significativas: el segmento basal apical vs. subcostal fue -16.5% (-21% a -11%) vs. -15.5% (-20% a -11%), p = 0.99, el segmento medio apical vs. la vista subcotal fue -16.5% (-21% a -12%) vs. a -16.5% (-20% a -11%), p = 0.87, el segmento apical vs. la vista subcostal fue -12% (-18% a -8%) frente a -13.5% (-19% a -10%), p = 0.93. Conclusión: En pacientes con HP, el SLVD obtenido en la pared libre subcostal es una alternativa útil en los casos con ventana acústica apical subóptima.

Corrigendum to "Unveiling molecular details behind improved activity at neutral to alkaline pH of an engineered DyP-type peroxidase" Comput Struct Biotechnol J, 20 (2022), 3899-3910.

[This corrects the article DOI: 10.1016/j.csbj.2022.07.032.].

Nanomechanical Filler Functionality Enables Ultralow Wear Polytetrafluoroethylene Composites.

Surprisingly, certain α-phase alumina filler particles at one to five weight percent can reduce the wear rate of polytetrafluoroethylene (PTFE) by 10,000 times, while other, seemingly comparable α-phase alumina particles provide only modest─by PTFE composite standards─100 times improvements. Detailed studies reveal that size, porosity, and composition of the particles play important roles, but a quantitative metric to support this mechanism is yet to be developed. We discovered the mechanistic importance of friability of the particles, for example, the ability of the particles to fragment at the sliding interface. This work establishes the importance of functionally friable metal-oxide filler particles in creating ultralow wear PTFE-metal-oxide composite systems. We used in situ nanoindentation/electron microscopy experiments to characterize the fracturability of candidate filler particles. A mechanistic framework relating apparent particle fracture toughness and wear is established, where porous low-apparent fracture toughness particles were observed to promote ultralow wear by breaking up during sliding and forming a thin, robust tribofilm, while dense, high-apparent fracture toughness particles abrade the countersurface, limiting the formation of ultralow wear promoting tribofilms. This framework enables use of a new metric to select filler particles for multifunctional, ultralow wear PTFE composites without relying solely on empirical tribological tests of polymer composite materials.

Increasing the Realism of in Silico pHLIP Peptide Models with a Novel pH Gradient CpHMD Method.

The pH-low insertion peptides (pHLIP) are pH-dependent membrane inserting peptides, whose function depends on the cell microenvironment acidity. Several peptide variants have been designed to improve upon the wt-sequence, particularly the state transition kinetics and the selectivity for tumor pH. The variant 3 (Var3) peptide is a 27 residue long peptide, with a key titrating residue (Asp-13) that, despite showing a modest performance in liposomes (pKins ∼ 5.0), excelled in tumor cell experiments. To help rationalize these results, we focused on the pH gradient in the cell membrane, which is one of the crucial properties that are not present in liposomes. We extended our CpHMD-L method and its pH replica-exchange (pHRE) implementation to include a pH gradient and mimic the pHLIP-membrane microenvironment in a cell where the internal pH is fixed (pH 7.2) and the external pH is allowed to change. We showed that, by properly modeling the pH-gradient, we can correctly predict the experimentally observed loss and gain of performance in tumor cells experiments by the wt and Var3 sequences, respectively. In sum, the pH gradient implementation allowed for more accurate and realistic pKa estimations and was a pivotal step in bridging the in silico data and the in vivo cell experiments.